1. Field of the Invention
This invention relates to a tape product used to drain static charge from personnel working in munitions and chemical plants and with sensitive electronic devices in circuit assembly areas, and in one aspect to a tape product which can be applied as a work surface covering, wall covering, rug or runner in areas where personnel are working with such devices to restrict damage due to static electricity.
2. Description of the Prior Art
Pads and mats for use in draining static charge from personnel are known and have been designed for use on work surfaces of various sorts. An example of such conductive mats is illustrated in U.S. Pat. No. 4,208,696 assigned to the assignee of this application. This patent affords an example of a web comprising a semiconductive polymeric surface layer, a conductive layer and a supporting substrate, for example, a resilient foam layer. This foam layer provides a cushioning when the web is used as a floor covering. Alternatively, a thin sheet of stiff plastic or fiberboard could be used in place of the foam, when the web is used under chairs and especially when used under chairs over carpeting. When the web was used as a floor mat, the thickness of the mat with the foam caused carts moving between work areas to bounce and the electronic parts contained therein to be jostled about. Further, soft mats would roll or wrinkle upon movement of a cart thereover, making the same not particularly desirable as floor coverings in the work areas.
The present invention provides a static dissipative covering for floors which does not have a height sufficient to cause a cart to be impeded in any way when rolling onto or off the covering. The tape of the present invention does not roll or wrinkle eliminating hazardous areas or areas where the material carts could be bounced during movement on, along, or off the same.
Another patent relating to static dissipative mats is U.S. Pat. No. 4,363,071 which discloses a multi-layer mat comprising an upper layer of low conductivity, in the order of 10.sup.8 ohms per square, bonded to a layer of greater conductivity in order of 10.sup.2 ohms per square, and a bottom layer of expanded polymeric material of relatively low conductivity, for example, an expanded version of the material of the upper layer. A further fabric base may be laminated to the bottom layer of the web as indicated in U.S. Pat. No. 4,414,260. The mat resulting had an overall thickness of 125 mils (3.175 mm) which has the same disadvantage of the web of the earlier patented construction, when used as a floor mat.
Further, in U.S. Pat. No. 4,219,602, and earlier issued U.S. Pat. No. 3,891,786, there is disclosed a sheeting material comprising an electrically conductive coating applied to a non-porous plastic substrate layer, the uncoated surface of which is then adhered to a second non-porous plastic layer by means of a plastisol adhesive. In one embodiment of U.S. Pat. No. 4,219,602 a reinforcing layer may be disposed within the plastisol adhesive layer. The fabrics produced by the invention of that patent were found suitable for use as mattress ticking, covers for wheeled stretcher pads, pillows, traction bags as well as other hospital applications. The thickness of the sheeting is said to comprise a 1/2 to 1 mil conductive layer and preferably a 2 to 4 mil (0.05 to 0.10 mm) non-conductive layer. This patent, U.S. Pat. No. 4,219,602 teaches a thin sheeting material but not a sheet material for controlled drainage of static charges. The earlier patent, U.S. Pat. No. 3,891,786, discloses a conductive sheeting comprising a polymeric film, which is perforated, laminated to a natural or synthetic rubber having up to 40% carbon black filler. The resultant product is conductive on the surface of the polymeric film.
U.S. Pat. No. 4,424,900 discloses a laminate material for use in the manufacture of packages and is approximately 2 mils (0.05 mm) thick comprising a polymeric substrate adhered to an anti-static polyolefin material, with a conductive layer of sputtered metal applied to either the substrate, having a volume resistivity of at least 10.sup.10 ohm-cm, or the anti-static layer, having a surface resistivity between 10.sup.6 to 10.sup.12 ohms per square. There is no teaching here of a tape material for use on a floor covering or that the adhesive layer should be covered by a removable liner to form a tape and surely such a product would be undesirable as a packaging material.
U.S. Pat. No. 3,904,929 discloses an electrodischarging sheet prepared by applying a carbon black-high molecular weight resin composition to a base material including woven, unwoven and knit clothes and paper having an affinity to the resin compositions The base material is porous and the material of this invention can be used for clothes, carpet or wall materials. A product of this invention was believed to have been sold as "NON-SPARK TAPE AND SHEET" and sold as a wrapping for piping, wherein at least one end of the tape product had an adhesive coating to adhere the end to the pipe.
The prior art references have thus provided teachings of various compositions of sheets, webs, mats, etc. serving to dissipate static charges which might build in the various areas. The need also for materials on the floor have been known, but the need for a material capable of discharging the static charges and yet not disrupt the normal flow of people and material carts has not been taught or recognized in the art. Therefore it is an object of the present invention to provide a tape in suitable widths to use as rugs or runners in work areas or as floor coverings in assembly areas to provide a static dissipative surface. The materials can also be used as wall and work surface coverings.